Filters are made in a number of materials, sometimes in combination with one another. Let’s take a look at some of the most common types of hydraulic filter media.
Cellulose is a widely abundant organic polymer that’s sourced mainly from wood pulp and cotton, and is relatively inexpensive to produce. However, its lack of uniform pore structure gives it a nominal rating, which can make cellulose filters susceptible to deterioration and shedding. While cellulose can capture particles, it’s less effective in retaining them, which along with shedding can lead to damage in industrial systems.
Glass media has a uniform pore structure, which gives it the ability to capture and contain more particles than cellulose. It’s not susceptible to structural manipulation, and it is immune from shedding, so that dirt stays where it is. For this reason, glass filters are awarded absolute ratings, and are considered an upgrade to systems that have been running on cellulose filters.
Made from stainless steel, wire mesh filter media have absolute ratings, however it is more durable than cellulose, and more capable of containing particulate. Wire mesh filters are ideal for fire-resistant fluid applications, such as high temperature governor controls, steel mill hydraulics and aircraft ground support equipment.
Coalescing filters are designed to separate two fluids from one another in different phases, while also filtering out particulate. Common in a variety of industries, coalescing filters are available in two subtypes: liquid-liquid filters, and liquid-gas filters, Coalescing filters can bring together into large drops free and emulsified water dispersed in oil and fuels. Those large drops can then be easily removed from the oil or fuel stream. Synthetic coalescing media now replace treated paper media for superior reliability.
Resin filter media treats fluids at a molecular level by removing contaminant molecules such as acids and free radicals, that form as a byproduct of fluid degradation and oxidation. Resin filters are designed to remove specific contaminants from fluids without removing additives, which results in better fluid performance.
High flowing lubrication systems found in many gas turbines create a static charge that builds up on filter elements until the charge jumps to a ground source. These very high temperature events ( 1000 deg F + ) burn the oil creating varnish which collects in servo valves causing failure. Non-spark filter medias are grounded so they don't build up a static charge, which improves equipment reliability and extends fluid life.
These filters are designed to prevent spark discharge, and therefore prevent oil degradation and antioxidant additive depletion while extending fluid life.
Water removal filter media is designed to remove small amounts of water from hydraulic systems. Water removal filters are typically divided between two types, coalescing and absorption.
Acid and Varnish Removal
Designed to remove the contaminants that accumulate in all lubricants and lubricating fluids, and ensure smoother operating systems.